AVR Eeprom Understanding

Question

I have started to create a button counter and was successful in doing that then I shifted myself to reading and writing eeprom I tried to use the eeprom to read and write a single byte and was also successful in doing so, pretty basic stuff. Recently I tried to use the eeprom_update_word function which is a little confusing to me as I think doesn't work quite well I had tried but was successful can someone help me? Below is what I have written:

 // removed the standard header as they aren't displayed here!

void lcd_num (int);


int main(void)
{
    uint16_t c = 0;
    DDRD = 0x00;

    lcd_init(LCD_DISP_ON);
    lcd_string(5, 0, "COUNTER");
    lcd_command(0xC5);
    // check if value has already been used/initialized...
    if (eeprom_read_word((uint16_t*)10) == UINT16_MAX)
    {
        // ...if not, init to 0
        eeprom_write_word((uint16_t*)10 , 0);
    }
    else
    {
        // ...if yes, read value back
        c = eeprom_read_word((uint16_t*)10);
    }
    lcd_data(c+48);

    while(1)
    {
        if( (PIND & 0x01) == 1 )
        {
            c++;
            lcd_command(0xC5);
            lcd_num(c);
            eeprom_update_word((uint16_t*)10, c);
            while( (PIND & 0x01) == 1 );
        }
        if((PIND & 0x02) == 1)
        {
            eeprom_write_word((uint16_t*)10,0);
            c = eeprom_read_word((uint16_t*)10);
            while((PIND & 0x02) == 1);
        }
    }
}



void lcd_num(int n){
    lcd_data((n/1000)+48);
    n %= 1000;

    lcd_data((n/100)+48);
    n %= 100;

    lcd_data((n/10)+48);
    n %= 10;

    lcd_data(n+48);
}
            void lcd_num(int n){
            lcd_data((n/1000)+48);
            n %= 1000;

            lcd_data((n/100)+48);
            n %= 100;

            lcd_data((n/10)+48);
            n %= 10;

            lcd_data(n+48);
        }

Can I ask for another favour here? I want to use a manual button to erase the eeprom so that I may not run out of space I have tried this but this doesn't work. Am i doing this correct ??

do you mean `eeprom_update_word` (used in the code) or `epprom_update_byte` (mentioned in explanation) ? — Z4-tier, Dec 09 '19 at 01:20
Oh, I am really sorry I have mistakenly typed eeprom_update_byte in the explanation it was supposed to be eeprom_update_word as mentioned in the code — user9728254, Dec 09 '19 at 02:24
Please take the [tour] and learn [ask]. Are you aware that you can [edit] your question? There is a small link on the right side below your question. — the busybee, Dec 09 '19 at 07:02
Are you sure that the port reads "1" when the button is down? Are there some pull-down resistor? — linuxfan says Reinstate Monica, Dec 09 '19 at 09:10
Yes , with this setup (code) the button reads one when pressed when reads zero when not pressed with no debounce at all.The first button works flawlessly you can try out yourself! — user9728254, Dec 09 '19 at 15:10

score 2 · Answer 1 · answered Dec 09 '19 at 07:04

2

Since all of your program is executed when powered on, this lines will run, too:

uint16_t c = 0;
// unrelated lines ...
eeprom_write_word((uint16_t*)10 ,c);

And they will overwrite the value you stored there before.

answered Dec 09 '19 at 07:04

the busybee

10,755
3
13
30

score 1 · Accepted Answer · answered Dec 09 '19 at 08:09

1

Currently, your counter value gets overwritten on each restart. You need to do some kind of check, whether the EEPROM location was already initialized (default EEPROM content is all 0xFF).

// check if value has already been used/initialized...
if (eeprom_read_word((uint16_t*)10) == UINT16_MAX)
{
    // ...if not, init to 0
    eeprom_write_word((uint16_t*)10 , 0);
} 
else 
{
    // ...if yes, read value back
    c = eeprom_read_word((uint16_t*)10);
}

answered Dec 09 '19 at 08:09

Rev

5,827
4
27
51

Oh thanks very much I had tried to use what I have written above but it doesn't even compile how great of you to check and solve the problem in one go.Thank you very much works perfectly.. – user9728254 Dec 09 '19 at 08:16

AVR Eeprom Understanding

2 Answers2